The present invention relates to particle counters of the impedance measurement type and more specifically to multiple probes in a hematology parameter measurement apparatus.
In the well-known liquid particle counter of the impedance measurement type, discussed here in the context of a hematology parameter measurement apparatus, a transducer may take the form of a conduit having an aperture in one wall and be provided with both an inner electrode within the conduit and an outer electrode. The transducer is immersed in a liquid sample and liquid is aspirated through the aperture into the probe. As particles pass through the aperture, the impedance between the inner and outer electrode increases, producing counting pulses. An example of such an apparatus is disclosed in U.S. Pat. No. 3,921,066 to Henry R. Angel and James W. Hennessey, issued Nov. 18, 1975. This patent is now assigned to the assignee herein, and the disclosure thereof is incorporated herein by reference. In the use of the apparatus disclosed therein and apparatus of other manufacturers intended for the same purpose, one transducer probe is provided for sequential counts of red and white blood cells. In blood cell counting, a blood sample is taken and a first dilution thereof having a ratio on the order of magnitude of 1:250 and a second dilution having a ratio to the original sample on the order of magnitude of 1:62,500 are respectively used for white blood cell counts and red blood cell counts. Lysing reagent is added to the white blood cell count sample to destroy red blood cells. Red blood cell count and white blood cell count dilutions may be measured in pairs for a plurality of patients, or red blood cell count samples and white blood cell count samples may be grouped. Due to the presence of lysing reagent in white blood cell count samples, it is necessary to rinse the transducer probe before running a red blood cell count following a white blood cell count. Thus, the instrument operator has the choice of separating the running of red blood cell counts and white blood cell counts for each patient, or to do both counts for one patient at a time. In the latter situation, a rinse must be performed before each red blood cell count measurement.
While prior art systems have been provided with separate sets of transducers for performing red blood cell counts and white blood cell counts, most notably the Coulter Counter.sup.R Models, such systems have been, in comparison to other hematology cell counting systems marketed to hematology laboratories, complex and expensive. Other multiple probe systems have been disclosed in the prior art such as in U.S. Pat. No. 3,444,464, issued May 13, 1969 to W. H. Coulter, et al. These systems have not provided for counts performed on a different dillution through each transducer aperture.